Abstract

We describe a simple technique for simultaneously imaging multiple
layers within an object field onto a single camera. The approach
uses a binary diffraction grating in which the lines are distorted such
that a different level of defocus is associated with each diffraction
order. The design of the gratings is discussed, and their ability
to image multiple object planes is validated
experimentally. Extension of the technique for spherical-aberration
correction is described, and it is shown how the gratings can be used
as part of a wave-front–sensing system.

Contour plot of the intensity in a meridional plane near
the focus of a combination of a quadratically distorted grating
(W20 = 1λ and a grating period of
631λ) and a lens with a single point source. The intensity of
each diffraction order is normalized to unity. Dimensionless units
of u = 2π(r/
f)2z/λ and
v = 2π(r/
f)y/λ. Contours are located at
0.9, 0.5, 0.1, 0.05, and 0.01.

Experimental images of a single object plane with the
camera positioned in image planes (a) 2, (b) 1, (c) 3, as
shown in Fig. 3(a). Because an amplitude grating was used, the
intensity of the nonzero orders was lower than that of the zero
order. The images are normalized by adjustment of the gray-level
scaling in each diffraction order to equalize their peak
intensities. The raw intensity in the three orders could be
equalized by use of a binary phase grating with a phase step of
0.639π.

Experimental images taken simultaneously on a single
camera by use of a defocus-grating–lens combination. The central
(zero-order) image shows the uniformly illuminated deformable
mirror surface. The left-hand (+1-order) image and the
right-hand (-1-order) image represent images of planes that are a
distance of approximately 1 m on either side of the mirror
surface. Four electrodes are switched on, causing four regions of
localized curvature.